Crepe processes, especially double recrepe (DRC) processes, have been used to produce paper products, such as paper towels and wipes, with specific properties. The DRC process involves creping a base sheet or nonwoven web on a drum, printing a polymeric binder on one side of the sheet, flash drying the binder, creping the base sheet on a drum again, printing a polymeric binder on the other side of the base sheet, flash drying the binder, and then creping the base sheet a third time. The base sheet is printed while traveling through gravure nip rolls. Various crepe processes and binding materials used in the processes are known. Examples of such processes are disclosed in U.S. Pat. No. 3,879,257, U.S. Pat. No. 3,903,342, U.S. Pat. No. 4,057,669, U.S. Pat. No. 5,674,590, and U.S. Pat. No 5,776,306.
In order for the base sheet or web to adhere adequately to the creping drum, polymeric binders used in creping processes are typically emulsion polymers containing surfactants that are based on alkylphenol ethoxylates (APEs). Known emulsion polymeric binders, that are free of alkylphenol ethoxylates, have not been effective in creping processes, especially DRC processes, because they do not provide the necessary adhesion to creping drums, produce an unacceptable amount of foam, are too low in viscosity, decompose at elevated temperatures, causing an unacceptable odor, and/or are subject to felt filling.
Appropriate binders for making paper products using a crepe process should be free of APE-based surfactants, adhere to a creping drum, provide a high degree of softness and absorbency to the finished product, and not felt-fill.
Heretofore, specific measurable properties for predicting the effectiveness of binders for a crepe process have not been reported.
This invention is directed to APE-free polymer binders formed by emulsion polymerization techniques and having a specific peel value and a specific cure profile. Binders having the peel value and cure profile described herein can be considered for use in crepe processes, especially DRC processes. According to this invention, the APE-free polymeric binders have a peel value, when adhered to a heated metal surface, of 35% to 200% of the peel value shown by a standard APE-based polymer binder control (i.e., AIRFLEX(copyright) 105 vinyl acetate-ethylene (VAE) polymer emulsion) and exhibit a cure profile such that at least 55% cure is achieved within 30 seconds at a temperature required for cure. Wet tensile strength is used to determine the cure profile. The peel value is determined by a modified release and adhesion test.
Binders having the properties described above are excellent candidates for use in crepe, especially DRC, processes. When used in making paper products, they should adhere to the creping drum providing a high degree of softness and absorbency to the finished paper product and not felt-fill; thus reducing production breaks, while ensuring that the desired finished product is manufactured.